State Water Resources Research Institute Program


Project Id: 2010DC115B
Title: Determination of Seasonal Source Variation of Hydrocarbons, Fatty Acids, Organics and Nutrients in the Anacostia River: Stable isotope Ratios of Specific Compounds
Project Type: Research
Start Date: 3/01/2010
End Date: 2/28/2011
Congressional District: DC
Focus Categories: Sediments, Toxic Substances, Ecology
Keywords: hydrocarbons, fatty acids, sediment biogeochemistry, compound specific stable isotope analysis
Principal Investigator: MacAvoy, Stephen E.
Federal Funds: $ 15,000
Non-Federal Matching Funds: $ 12,274
Abstract: Organic contamination appears to be delivered to the Anacostia River via runoff associated with episodic precipitation events. The contamination includes PCBs, PAHs and nutrients, which appear to be derived both from point sources (i.e. combined sewage outflows) and non-point sources (runoff from the watershed impermeable surfaces). Although the presence of contaminants and nutrients has been well established, their seasonal distribution and changes in source importance with variable hydrology associated with season has not been well documented.

Given that the biological response of invertebrate and bacterial communities to episodic contamination versus chronic contamination are likely be different, it is important to better understand the seasonal changes in those contaminates and nutrients. Additionally, it is also important to determine changes in nutrient plus contaminant sources with season and river discharge. Organic materials may be derived from different sources and may undergo transformations if reworked (metabolized) by bacteria. For example, a twenty-carbon fatty acid (FA) may be normally associated with algal production, yet it may have originated from a longer fatty acid of terrestrial origin that was reworked by bacteria. If that reworking could be quantified, then the origins of the original FA determined and the role of bacteria better understood. Likewise, if nutrient sources to heterotrophic bacteria during changing seasonal hydrological conditions could be characterized, it would be easier to understand the importance of runoff in bacterial or algal productivity.

The objectives of this research are 1) to determine the sources and biochemical transformation of fatty acids in the river, and 2) to assess seasonal variation and river discharge relationship to nutrient sources in the river. This work will involve 1) isolating fatty acids from the water column, sediment and invertebrates from four Anacostia sites and determining the carbon isotope ratios of the specific fatty acids, and 2) assessing petroleum derived hydrocarbon distribution and composition at sites throughout the Anacostia river system. Sites will be chosen from upstream branches through downstream locations and the sediment will be sampled for microbial and chemical characteristics. Using characterizing organic hydrocarbons and stable isotope ratios the flow of carbon through the river will be traced. Chemical analyses of the bulk sediment, filtered water and invertebrate tissues will include analyses for alkanes and the stable isotopes of carbon, sulfur and nitrogen. Through our research, we will be able to provide information on areas of active bacterial production. Second, our studies will enhance the knowledge on distributions and locations of other organic contaminants, such as alkanes. Third, by having students as an important component of our Anacostia River research we are not only advancing the future of science in this region, but also enhancing basic knowledge about this important river in the nation's capitol.

Progress/Completion Report, 2010, PDF

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